Hyperfixation last for years

Hi I have this obsession about one topic and it. Continue for years first I found out about atheism and then bye time I couldn't stop thinking about it or searching or talk about it with everyone then after 2 years im just not interested anymore and strated to be obsessed with psychiatry for 3 years until now my question is is this hyperfixation or monotropism or special interest.

If it's hyperfixation then how? It last weeks not years